Method for the preparation of titanium dioxide



Leon Ma k r," evtfjfork, N g schied; Ma on-en, N.

i -"Lead'C0n'ipai1y, New York for making thesain'e.

of New Jcr sey The present invention adapted for use as 'a sta-rt-i material for-the preparation of rutile 'single crystal-f-boules, by

a I if H l .fe a cto Serial No. 54,573 wa p -\4., int,

aims. (Cl;2 3 '202 relates-ta a novel m m: :lmum I dioxide composition ;off i matter especially l ofocesses embodying 'the principles of"Verr'1euil,-or 'Iiiodifications"of suchprocesses; and to-methods f I'n='copending application, Serial"Number 54,-562, I filed oc'tober '14, 194,8; there is described a method for the preparationof rutile single crystal-.boules.

In that application; it is shown that by mainta'ining' certainmonditions heretofore. unappreciated, it is possible to prepare rutile single crystal boules. one-such-condition is the purity of sti l at tenium di i starti ate ial; I t is I sential that the starting material befreepnat least substantially freefrom elements possessing ionic radii incompatible with the rutile crystal latticei The ionic radiioftetravalent titanium cis'reportedz-to be .0..68.Angstrom-: unit and" it: has

Ibeen found that elements having ionic ira'dii of :less than about 0.60 Angstromeunit andgrea-ter ;,than: about 0.75 Angstrom?v uniti should jnotyxbe I hibit the formation of the rutile single crystal.

Furthermore, the starting material should be free or at least substantially free from elements which react with titanium, or titanium dioxide to form chemical compounds. The compounds 'formed from suchlelements crystallize in their own distinctive pattern, incompatible with the rutile single crystal. Thus, magnesium which has an ionic radii within the specified range and would, therefore, ordinarily be compatible is unacceptable because it forms with sium titanate.

Impurities which commonly occur in titanium dioxide but which are incompatible with the rutile crystal are principally silicon, magnesium, and lead, and these in general should not be present in amounts greater than 0.15% silicon, calculated as SiOz; 0.005% magnesium, calcu- TiOz, magnelated as MgO; and 0.002% lead, calculated as PbO. In this connection, however, itshould be pointed out that some amount of compatible 0.3% total-incompatibleimpurities.

' elements which maybe-'presentin the T102 startingmaterial as impurities onadded as suchto impart *a desired-color to the final rutile -crystal ma'y' act as solventsfor elements which-are #incompatiblefithereby raising the minimum amount of such impurities-"-which may beapresen't without preventing formationof the rutile single" crystal boulek Thus; v'anadium and iron-,- whichimparts =to the final rutile crystaldefinitecolorationswill tend to raise the tolerancetowardsilicon. It will be appreciated that-a maximum: upper limit for the content of incompatibleiimpurities cannot :be --;precisely:given; but for the production ofta' rutile single crystal boule' having a maximum purity and a :in'inimum of internal; stresses, the'..:TiO2

starting-,- material should her. free i or at least substan-tially free from incompatible I impurities, as L. explained v above.e 1A satisfactory -.TiO2 starting ==material for'the preparation; of rutilesinglescrystale boulesl shouldnotzcontain more (than about The present inventionacontemplates finelydivided ;Ti0ziwhich is free; or: at least. substantially freeifromimore than a1traceofielementsihaving I denier-radii; incompatible "with the rutile crystal .lattice as; well as elements which react with titaniumuo itanium'a'dioxide to form chemical compounds, The invention further: contemplates methods for the production; of such. titanium .di-

oxide.

According to one preferredmethod for producing the novel titanium dioxide of the present invention, a titanium compound is reacted with an ammonium salt to form the complex double ammonium-titanium-sulfate which is then decomposed by heating at an elevated temperature leaving a residue of pure, finely-divided titanium dioxide of the present invention. The preparation of the ammonium-titaniumsulfate may be carried out in any convenient manner. It is preferred, however, to react'titanium tetrachloride with ammonium sulfate. When carrying out the invention according to' this embodiment,v undiluted relatively pure titanium tetrachloride is added to a saturated soluble ammonium-titanium-sulfate precipitates im-- mediately upon the introduction of thetitanium tetrachloride .to the ammonium sulfate and is then recovered from the supernatant hy'drochlo-' ric acid liquor. It should be purified preferably between 0.1 mioronv and" 02 growth: begins at about: '900" 1 andntlie 'material is completely: eonverted to rutile t temperatures about 000 20. GenerallyzspeagkingutheTinventicin hydrate obtained by the hydrolysis of titanium sulfate solutions. The titanyl sulfate, TiOSOZ; is preferably admixed with an equalgamount pf ammonium-su1fate-solution,

The double ammonium titaniurn V also be prepared from a solution oit tanium sul-l fate or an ilmenite solution having a'varynig molar ratio of TiOz to H2804. However, for the 5 best result and greatest yieldithe double fsaltshould be prepared either from titanium "tetra-- chloride or titanyl sulfate. Having preparedvthe" crude amonium-titaniurn-sulfate, it is then del a e o :nu w t' r e bly b :x ryst l a- 20 eni c eer. si meet he re iredd er qfli l mentioned impurity tolerances, -Theiam omum ti-tanimn-sulfate is dissolved in dilute sulfuric tanium: dioxide starting-"i material suitable for- 'the s manufactured-single crystal ruti'le :bou1es.'-

The "decomposition ='of uthez-iammor iium -titamum sulfate' "may be -carriedflout 'at temperatures rangingifromi'about d50b C.x;to 1l0,0-i6. Between 5 850? O. gand- 900 C. there resultssa 'fltitaniur n dioxide of an ultimateaunit p'artiole si ze 'averagifig r-micron: Crystal should be "operated in such vinannr ias to' obtain from the decomposition of 'rthe afrfmonium-titanuim sulfaterrutile titanium dioxideg aViiIg' tF-ie s'mallestzpossible ultimatehmit parmiesme contreatment for about 1 2 hours The product obamdpe ses'ses an opeh strutuiuand has a "spongeuke'or filifiy a pearance."-

The foregoing description has been given for purposes of illustration, but the invention is not ="to be'i limitdithereto and various modifications water, and the resulting mixture adde'cl to the '10:;

and variations within the scope of the appended claims maybe employed.

thod -fo {the preparation of titanium d1- oxidvhaving -an ultimate unit particle size not in excess of about 0.5 micron and capable of id ming"upc n-fiision rutile single crystals which comprises calcining ammonium-titanium-sulfate at temperatures between about 850 C. and about 1100? C. until the ammonium and sulfate conit entsa stant eem l rre qr d by and; the residual titanium dioxide stal m ur i l r. ,v r e. re a et ap a a -d oxide' having an ultimate unitparticle size not in :excessof about 0.5 micron and-capablegeffor ming upon fusion rutile single crystals-which com- ==prises-- calcining 5' ammonium titanium sulfate at temperatures between about1850 C-.- and-900 C. ion'from about one H0111 CO73gbUtllb'hW0 -h0l1l8r.

ESPENSCHGYED.

The roiwwm'g rerereaces 'a're of restra nine emmnsmm ba aars Date Y Number Name "REFERENCE? 7 Gems and: GemvM'aterials "by 'Krausiarid 

1. METHOD FOR THE PREPARATION OF TITANIUM DIOXIDE HAVING AN ULTIMATE UNIT PARTICLE SIZE NOT IN EXCESS OF ABOUT 0.5 MICRON AND CAPABLE OF FORMING UPON FUSION RUTILE SINGLE CRYSTALS WHICH COMPRISES CALCINING AMMONIUM-TITANTIUM-SULFATE AT TEMPERATURES BETWEEN ABOUT 850*C. SAID ABOUT 1100*C. UNTIL THE AMMONIUM AND SULFATE CONSTITUENTS ARE SUBSTANTIALLY COMPLETELY REMOVED BY VIOLATIZATION AND THE RESIDUAL TITANIUM DIOXIDE HAS THE RUTILE CRYSTAL STRUCTURE. 